The present invention relates to head up displays for motor vehicles.
It has been proposed to provide a head up display for a motor vehicle in which an enhanced view of the road ahead is projected onto the vehicle windscreen, so that it is overlaid onto the drivers view of the scene. In this manner, potential hazards which may not be clearly visible to the driver, may be highlighted.
In order to ensure that the objects within the image appear to the driver to be the same size as the objects in the real scene, the field of view of the sensor is matched to the field of view which the driver has of the display. The image is then projected into the relevant area of the driver's forward line of sight and is arranged such that the driver's own view of the objects is overlaid with the images of the objects generated from the sensor, processing and display combinations.
To produce an overlaid image of this type, a large field of view is required. Within the constraints of the motor vehicle which places limitations on the size of the video display device which may be used and the optical path length of the projected image, this may be achieved by the use of a mirror which will bend the optical path. This will also allow the display device to be positioned behind the dashboard of a vehicle, the mirror serving to deflect the projected image onto the windscreen.
The centre line of the projected image and the centre line of the driver's forward field of view must also be coincident. As a result, the mirror used to deflect the projected image onto the windscreen must be positioned directly in front of the driver at a level below the level of the windscreen. That is, in a position conventionally used for the vehicle instrument display. The positioning of a mirror in this way will consequently significantly reduce the area available for vehicle instrument display.